Advances in technology have opened up many opportunities for applications that go beyond the traditional ways of doing business. Electronic commerce over the Internet has become widely accepted, requiring many companies to either install one or more servers to host a web site and maintain accessible databases or to contract with data centers to provide such services. Important functional characteristics for these servers include reliability, availability and serviceability.
A loss of power adversely effects the availability of a server, which is especially costly when such power loss occurs for a server that is responsible for handling mission critical applications. To enhance availability during a power loss condition, critical servers may be equipped with back-up power functionality to allow that server to save its operational states before power-down. Availability may further be enhanced by supporting hibernate.
Initiated by an operating system (OS) of the server, “Hibernate” is a low-power, long wakeup-latency sleeping state where server hardware has powered off most devices. Hibernate is also referred to as “S4” in accordance with terminology set forth by the Advanced Configuration and Power Interface (ACPI) Specification (Version 2.0) published Jul. 27, 2000.
Prior to entering Hibernate, various hardware states of the server as well as its stored contents are copied and stored as an image on its hard disk. Hence, during a wakeup operation, the server may be quickly restored to an operating state that existed prior to entering Hibernate. For correct operation, the OS expects to see the same hardware configuration on resume as was prior to hibernate. However, hot-plug capable multi-node architectures normally do not conduct Hibernate operations for a variety of reasons.
One reason is that, to allow maximum availability, multi-processor servers should conduct boot operations is a non-deterministic manner. In other words, the selection of which processor controls a platform boot operation at one point in time may differ from which processor is selected at a later point in time. As a result, the configuration of the platform after resuming from Hibernate is not guaranteed to match its pre-Hibernate configuration at a first time period.
For example, the order in which nodes of the platform are recognized by the operating system (OS) of the platform at the first time period may differ from how these nodes are recognized by the OS at the second time period. Each node being a collection of interconnected components. Thus, if the nodes differ, the logical identifier (ID) for processors assigned by the OS would differ, which greatly complicates returning the platform back to its pre-Hibernate configuration. Moreover, the amount of memory assigned to a particular node may differ (since the boot node may be different) and the number of processors on the boot node may be different (since the boot node may be different).